This invention is directed particularly to the problem of winding or wrapping magnet coils with superconducting cable or ribbon. In addition to being very expensive, superconducting cable is extremely sensitive to mechanical mistreatment, such as being stretched or jerked. Such mistreatment reduces the current-carrying cross sectional area of the cable along the length that has been subject to abuse. Superconductors can carry many thousands of amperes per square centimeter, but if the current-carrying capacity is exceeded, due to any unexpected reduction in cross sectional area in a length that has been stretched, that length may suddenly go into normal or resistive conductivity, rather than superconductivity, as the current is increased to its supposedly safe value. When this happens, heat is generated in the resistance of the cable, with the result that a very expensive coil can be badly damaged or completely destroyed. Most superconducting magnet coils are hand wound, which necessarily entails a variable winding rate and sudden stops and starts. Sometimes, one or two turns must be removed and rewound. For these reasons, it is extremely important that tension be maintained in the superconducting cable under all of the conditions of variable and intermittent demand, associated with hand winding. Moreover, it is important to maintain the tension as constant as possible at the desired value, to avoid stretching of the cable.